December 2007
Special Report

Rig Floor Equipment: Top drive's ac motor eliminates gearbox problems

LeTourneau Technologie (LTI) Drilling Systems (formerly LEWCO) designed the DirectDrive line, its new top drive system requiring no gearbox.

Vol. 228 No. 12  


Top drive’s ac motor eliminates gearbox problems

Looking to move top drive technology past the problems encountered with conventional gearbox-driven top drives, LeTourneau Technologie (LTI) Drilling Systems (formerly LEWCO) designed the DirectDrive line, its new top drive system requiring no gearbox. The core difference between the company’s new line of top drives and conventional systems is its elimination of problematic gearboxes. To replace the function of the gearbox, the company uses a patented AC motor which provides both power and control. Many of the problems encountered with top drive gearboxes result from their basic design, which must include large numbers of moving parts, along with bearings, seals, and associated lubrication systems. The basic design of the DirectDrive system eliminates all of these potential problems.

The top drive is a fully integrated system, available in 250, 350, 500, and 1000 models. This system is designed around its patented Power Systems through-shaft design AC drilling motor. This high-torque, AC-traction motor, aptly named the PowerTorque, is designed specifically for top drive applications. The top drive’s AC motors are built using more iron and copper content than conventional AC motors, which contributes to their ability to generate more torque, from zero RPM through rated RPM. This rugged, heavy metal construction provides additional thermal mass, providing these motors with the capability to withstand the higher temperatures that can result from continuous low-speed, high-torque drilling.

Fig. 1. LTI’s patented AC motor provides controls as well as power. 


Fig. 2. Fluid path through the DirectDrive top drive. 

The top drive system is manufactured and tested to API 8C PSL1 standards. The system also offers a number of other features such as a pneumatic counterbalance system, integral disc brakes, and a pipe-handling system with dual-drive, 360° rotational capacity. In addition, it allows main stem assembly replacement without having to remove the motor or having to unrig, thereby reducing the downtime normally required for servicing.

Currently, there are five model L-DDTD-500 top drives in use. Three of these are working for the Rowan Co. in the Kermit/Pecos region of West Texas, where they are drilling to about 18,000 ft. Another of these top drives is working in south Louisiana, where it will be drilling to about 16,000 ft. The final one is installed on Rowan Rig 68, working in a particularly demanding drilling operation in Alaska. This job calls for numerous lateral drilling operations to almost 24,000 ft. This application has required around 30,000 lb of continuous torque, which the top drive system has reliably withstood throughout the project. In addition, the company will soon be supplying more of its top drives worldwide. Burgan Co. of Kuwait will be using a 500-ton top drive, and Eurasia Energy Ltd. has ordered two 500-ton top drives for its rigs in Russia. WO


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